A universal motor can operate on both AC and DC power. It is a commutated series-wound motor with a commutator that connects the stator's field coils in series with the rotor windings. Universal motors are sometimes known as an AC series motor. Universal motors can operate well on AC because the current in both the field coils and the armature (and their respective magnetic fields) will alternate (reverse polarity) synchronously with the supply. The resulting mechanical torque will occur in a consistent direction of rotation, independent of the direction of applied voltage. The developed torque is determined by the commutator and polarity of the field coils.
Universal motors can have high starting torque, can run at high speed, and can be lightweight and compact. They are commonly used in portable power tools and household appliances. Universal motors are also relatively easy to control electronically or via selectively tapping various coil points.